Crimea has been occupied for a decade, it's hardly an active warzone.
And they aren't crossing into enemy territory. People live there. And lots of them are Russian, including the authorities.
And finally, a beach might just be the safest place in Ukraine. What do you think is going to happen?
Ukraine had a decent navy until Russia captured or sank most of it. Their flagship was scuttled as well.
Also, concrete ships are a thing. They were popular during WWII due to steel shortages.